1. Field of the Invention
This invention relates to an efficient technique for cooling the target of a rotating anode x-ray source.
2. Prior Art
High power x-ray tubes may be used in applications relating to x-ray difraction topography, fine line lithography, radiography, etc. One way to increase the brilliance or load per unit area of an x-ray tube is to continuously position the electron beam focus on a freshly cooled metal target face. A suitable technique for increasing brilliance is to select an x-ray tube having a movable (i.e. rotary) anode target and an induction motor to provide anode rotation. However, for an x-ray tube to undergo continuous operation, an efficient cooling technique must be incorporated therein, inasmuch as the average temperature of the target surface is proportional to the input power, and the allowable load of the rotating anode target is determined, in part, by the melting point of the electron beam metal target surface. Two essential features of a rotary anode design include a water circulating mechanism for cooling the electron beam target surface and a vacuum sealing mechanism.
Typically, a direct cooling technique is utilized in the prior art for cooling the rotating anode target surface with a stream of water. However, the prior art direct cooling technique requires coolant channels to be radially extended throughout the rotating anode target. This has the undesirable effect of increasing the hydrostatic pressure at the electron beam target surface. As a consequence of increased hydrostatic pressure, the anode target size is restricted and the input power and temperature are limited which, in turn, undesirably reduces output brilliance. Moreover, due to the prior art mechanism for feeding cooling water to the interior of the target, the circumferential velocity of the rotating anode target is limited. What is more, much of the cooling water is ultimately disposed of and wasted.